1. Field of the Invention
The present invention relates to a portable communication system using a headset for calling to which a headphone and a microphone are attached, and a headset calling method. Particularly, the present invention relates to a headset, a portable communication system using the headset, and a headset calling method suitable for hands-free calling using a portable communication terminal.
2. Description of the Related Art
When making a call using a portable communication terminal, for example, a portable phone, a PHS (Personal Handy-phone System), etc., normally a caller holds a terminal in hand near his/her head. In order to eliminate this inconvenience, recently, a headset and a portable terminal are used in combination in some cases. That is, a caller is able to make a hands-free call by attaching a headset to his/her head and connecting the headset and a portable communication terminal with a cable.
Recently, a technique called Bluetooth has made its debut. By using the Bluetooth technique, it is possible for a relatively small type information processing device or portable communication terminal to transmit/receive speech and data at a high transmission rate of 1 Mbps by radio waves. The Bluetooth has, in comparison to infrared communication, advantages that power consumption is small and that communication is not blocked by obstacles when the distance between devices is about 10 m or less.
Recently, development of a chipset designed specially for the Bluetooth is positively being promoted. Accompanying this, various portable communication terminals using the Bluetooth have appeared. Due to this, it has become possible to perform radio communication with a headset having a built-in chipset for the Bluetooth. As a consequence, it becomes no longer necessary to connect a cable between a portable communication terminal and a device, therefore, a user is not restricted by the length of the cable in respect to the sphere of activity when using a portable communication terminal. Such advantages of the Bluetooth technique have been recognized and researches on communication devices using the Bluetooth technique have become more and more positive.
FIG. 14 shows a case where a portable communication terminal operates as an audio gateway as an example. A portable communication terminal 101 and a headset 103 incorporate therein chipsets 102 and 103 for the Bluetooth, respectively. The portable communication terminal 101 is connected to a mobile network 105 such as W-CDMA and GSM and able to receive necessary music data from a music distribution server in addition to performing telephone communication. By connecting the headset 103 and the portable communication terminal 101 with a Bluetooth communication channel 106, it is possible for a user to listen to the music data stored in the portable communication terminal 101 through the headset 103 by directing replay or stop of the music from the headset 103.
In addition thereto, by connecting the portable communication terminal 101 to an audio device of a vehicle including a speaker, it is possible to realize a hands-free voice response. Furthermore, applications of the Bluetooth are researched in order to realize file transfer between the portable communication terminal 101 and a personal computer or a communication device such as a PDA (Personal Digital Assistant) and synchronization of operations between these devices.
Thereupon, in the prior art, the portable communication terminal 101 is constituted so as to be connected only to the mobile network 105. As represented by the W-CDMA (Wideband Code Division Multiple Access) system and the GSM (Global System for Mobile) system, a portable communication terminal performs communication by using only a mobile communication network.
In contrast, a portable communication terminal capable of selecting not only the mobile network 105 but also a fixed network has been proposed. For example, Japanese Patent Application Laid-Open No. HEI 07-143553 (Document 1) has proposed such a portable communication terminal. The portable communication terminal described in the Document 1 comprises a radio channel control circuit for performing communication with a radio base station in a mobile network, a cable control circuit for performing communication with a terminal station in a fixed network, a channel switching circuit for selecting one of the two control circuits, and a charged capacity monitor unit for monitoring the charged capacity of its battery. The portable communication terminal is connected to the fixed network with a cable. When the charged capacity of the portable communication terminal drops and radio communication becomes difficult to continue, the channel switching circuit switches the channels from a radio side to a cable side, thereby it is possible for the portable communication terminal to continue communication through cable communication.
By partially utilizing a fixed network, it is possible to reduce communication costs. For example, let's consider a case of connecting a portable communication terminal to a fixed network via an access point provided in the interior by using the portable communication terminal mounted with a chipset for the Bluetooth. In this case, it becomes possible to reduce communication costs compared to the case where a call is made using only a rather expensive mobile network. Further, it is also effective for reduction in communication costs to connect a portable communication terminal to a fixed network through a wireless LAN (Local Area Network).
As described above, by also using with a fixed communication network, a subscriber of a portable communication terminal can receive a merit that it is possible to receive services of high quality while reducing communication costs. On the mobile communication operation company side, income from communication costs decreases by those corresponding to the costs by a fixed network. However, it is possible for the mobile communication operation company to obtain a larger number of subscribers by providing the merit of low-cost service.
By the way, there may be a case where a portable communication terminal is out of the area of radio communication, of course there may also be a case where the portable communication terminal is near a user, when the user of the portable communication terminal moves about in a office etc. with a headset attached on the request for hand-free calling. According to the conventional proposal described in Document 1, the relationship between a fixed network and a mobile network is considered only for a portable communication terminal, and no consideration with a headset included is made. Because of this, in an attempt to utilize a fixed network in a portable communication system with a headset included, there may occur a case where switching between a mobile network and a fixed network does not function properly.